Blow molding machines conventionally provide a parison, i.e. a tube of hot plastic, between open sections of a mold. Closing of the mold then clamps the parison and allows air to be blown into the parison such that it assumes the shape of the mold. After suitable cooling has taken place, the mold sections are opened to allow ejection of the molded part.
Blow molded parts such as containers have conventionally included paper labels that are glued thereto after the molding to identify the contents of the container to the consumer. One problem is that such paper labels can become wrinkled if dampened and can also become detached from the container if a waterproof glue is not used. Also, paper labels require a separate labeling step after the molding which thus adds to the cost of the container.
In-mold labeling has been developed in the recent past to provide superior bonding of labels to blow molded plastic parts. This in-mold labeling is performed by initially inserting a label within the mold prior to the introduction of the parison and by then closing sections of the mold in preparation for the blowing operation. The subsequent blowing operation forms the parison around the label to the shape of the mold and provides a permanent bond which is incapable of being broken by moisture or otherwise. Also, such in-mold labeling provides a smooth transition between the label and the adjacent surface of the molded plastic part and further provides additional strength since the label cooperates with the plastic in resisting deformation. Such strengthening also allows the use of less plastic to blow mold the part and thereby reduces the ultimate cost to the consumer. Furthermore, when utilized with containers for carbonated or other beverages, it is believed that in-mold labeling reduces the flow of carbon dioxide and other fluids through the container wall over a period of time and thereby increases the shelf life.
Prior in-mold label dispensers for blow molding machines conventionally include a label carrier having a vacuum cup that receives a label from a label magazine and is then moved to deposit the label within the mold cavity whereupon termination of a vacuum drawn at the suction cup allows a vacuum drawn at the mold cavity to secure the label in position in preparation for the blow molding. Such vacuum type label carriers have previously been mounted on linkages that move the labels in an angular path with respect to the direction of opening and closing movement of mold sections of the mold in order to permit depositing of the labels in the confined space permitted by the extent of the mold opening. With the linkage type of label carrier, only one label can be deposited within the mold at a given time since movement thereof on the linkage toward one mold section interferes with movement of a similar linkage toward an opposed mold section for depositing another label.
Another prior art type of in-mold label dispenser is disclosed by U.S. Pats. Nos. 4,355,967 and 4,359,314 and includes a label carrier that is moved along an abruptly curved path by a complex linkage which executes a 180 degree turn in order to transfer labels from a label magazine to the mold in preparation for molding. With this complex linkage type label dispenser, it is likewise not possible to deposit more than one label in the mold at a given time due to the limited space present upon opening of the mold.
U.S. Pats. Nos. 3,292,209, 4,397,625, and 4,498,854 disclose in-mold label dispensers wherein fluid motors move label carriages and/or label carriers on the carriages to transfer labels from label stacks into associated molds.
U.S. Pat. No. 3,324,508 discloses an in-mold label dispenser wherein a linkage moves labels from rolls of labels to a mold where the labels are held by an electrostatic charge prior to the blow molding operation.
U.S. Pats. No. 4,479,770 and 4,479,771 of William A. Slat, et al disclose in-mold label dispensers wherein a first solid mechanical drive moves a dispensing head between inserted and withdrawn positions with respect to an open mold and wherein a second solid mechanical drive extends and retracts label carriers in order to perform the labeling operation. Use of such solid mechanical drives to move the dispensing head and the label carriers permits accurate positioning of the labels.
U.S. Pat. No. 4,479,644 discloses another type of in-mold label dispenser for use with a plastic blow molding machine.
Certain plastic blow molds are constructed such that an elongated guide extending between the opposite sides of the mold provides support for the movable dispensing head or carriage in which the label carriers are mounted. Normally the dispensing head or carriage is pivoted about the guide to provide movement of the label carriers to the label transfer position where the labels are released and secured to the mold by vacuum. However, with certain mold constructions, there is insufficient room to position an elongated guide extending between the opposite sides of the mold and still permit the movement of the label carriers to the label transfer position in the inserted position between the open mold cavities. While it is possible to support the dispensing head or carriage in a cantilevered fashion for movement to the inserted position for depositing the labels, this results in a decreased accuracy in label placement and a resultant decrease in quality of the labeled product after the blow molding.